Basic streptococcal superantigens (SPEX/SMEZ or SPEC) are responsible for the mitogenic activity of the so-called mitogenic factor (MF)

The mitogenic factor (MF) of group A streptococci has been reported to be a superantigen stimulating human T cells carrying V beta2, 4 and 8 and has b een designated streptococcal pyrogenic exotoxin F (SPEF). MF was also shown to possess DNase activity. Here we have purified MF from culture supernata nts of different Streptococcus pyogenes strains. Surprisingly. the MF prepa rations from different strains showed different VP specificities depending on the expression of SPEC or SMEZ3 by the producing strain. Their mitogenic activity decreased upon Further purification. In addition, the mitogenic a ctivity could be only neutralized by antibodies against the basic streptoco ccal superantigens SPEC or SPEX (SMEZ3) but not by antibodies against MF it self although the latter were able to neutralize completely the DNase activ ity of MF. We Found that streptodornase type B (SDB) was expressed in two m olecular forms (SDBI and SDBII), differing only by one additional N-termina l arginine at SDBI. MF was found identical to the enzyme SDBII but is devoi d of superantigenic properties and should no longer be called a superantige n or a pyrogenic exotoxin. (C) 2001 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.